Growth factors reverse the impaired sprouting of microvessels from aged mice

Aging is accompanied by impaired angiogenesis and deficient expression of several angiogenic growth factors. To test the hypothesis that replacement of these factors would improve angiogenesis in aged animals, we cultured microvessels derived from the epididymal fat pad of aged and young mice ("aged" and "young" microvessels) in three-dimensional collagen gels for 2 weeks and measured their sprouting (formation of branch points) in response to fetal bovine serum (FBS), endothelial cell growth supplement (ECGS), and the specific growth factors transforming growth factor-beta1 (TGF-beta1), vascular endothelial growth factor (VEGF), insulin-like growth factor-1 (IGF-1), and basic fibroblast growth factor (bFGF). In the presence of culture medium with 1% FBS (Minimal medium), sprouting of aged microvessels was significantly less than sprouting of young microvessels. The addition of high levels of FBS and ECGS to Minimal medium enhanced the sprouting of microvessels from aged mice to a greater degree than that of young mice, such that the difference between the two age groups was no longer significant. Formation of branch points by aged microvessels was also significantly increased by Minimal medium supplemented with TGF-beta1, bFGF, IGF-1, or VEGF (listed in order of highest to lowest stimulation). Sprouts generated in the presence of VEGF possessed a particularly high percentage of endothelial cells. Mitomycin C did not diminish the degree of sprouting induced by TGF-beta1, VEGF, or IGF-1, a result indicating that early stages of angiogenesis, including formation of branch points, do not require cell division. From our findings in vitro, we propose that age-related deficiencies in angiogenesis in vivo are likely to be due, in part, to a decrease in angiogenic growth factors in the extracellular milieu.